1. Field of the Invention
The present invention relates to a camera module and an imaging apparatus incorporated in a mobile terminal and other small electronic apparatus, and particularly to a camera module and an imaging apparatus whose sizes are reduced by simplifying the configuration of a movable lens actuator.
2. Description of the Related Art
A small, thin camera module is incorporated in a mobile phone, a PDA (Personal Digital Assistant), and other small information processing apparatus. A camera module of this type needs to be smaller and thinner in order to meet demands for further reduction in size and thickness of such small information processing apparatus. To achieve the reduction in size and thickness, some camera modules employ a polymer actuator as a movable lens actuator (see JP-A-2006-293007).
To move a focusing lens or any other movable lens in a camera module in the optical axis direction, it is typically essential to increase the magnitude of thrust force and the response speed of the actuator. The load acting on the actuator increases, for example, in the following situations: when the weight of a movable lens increases; when the reaction force of a slidable member increases; and when the elasticity of a spring increases. When eccentricity of the lens is taken into account, in particular, it is necessary to support the movable lens by using a shaft so that the lens can be moved in the optical axis direction. In this case, friction between the shaft and a sliding hole on the movable lens side also increases.
To drive a movable lens in a camera module, it is therefore necessary to output a thrust force greater than or equal to the load described above. It is further desirable at the same time, for example, to achieve autofocus at a fast drive response speed.
A polymer actuator, however, has a small magnitude of thrust force because the actuator itself is soft by nature. The response speed of a polymer actuator is proportional to a voltage fed thereto, but the applied voltage decreases with distance from a voltage feed point due to resistance distributed across a membrane of the polymer actuator, resulting in decrease in the response speed.
JP-A-2006-293007 does not solve the problem described above because it employs a structure having two shafts. In this case, the response speed decreases because friction is produced between the shafts and sliding holes of a lens holder and electric power is fed to a polymer actuator only on one side.